Hydrophilic or partially hydrophilic plastic materials have been used in making "soft" contact lenses. For example, U.S. Pat. Nos. 3,503,393 and 2,976,576 describe processes for producing three dimensional hydrophilic polymers of polyhydroxyethylmethacrylate in aqueous reaction media; these polymers have low degrees of cross-linking in their hydrogel structure and have the appearance of elastic, soft, transparent hydrogels. Soft contact lenses have also been made out of silicone and other optically suitable flexible materials. The popularity of soft contact lenses is growing rapidly. The major virtues of these lenses are their softness (providing comfort to the wearer), permeability to gases, and their optical suitability. The hydrophilic lenses are particularly useful for ophthalmological applications due to their ability to absorb water with a concomitant swelling to a soft mass of extremely good mechanical strength, their complete transparency, and their ability to retain shape and dimension when equilibrated in a given fluid.
One very basic problem associated with soft contact lenses is the development of a convenient, safe and effective method for disinfecting and cleaning them. The fact that these lenses are hydrophilic (compared with hard contact lenses) makes them a good environment for breeding microbial contamination; this requires that the lenses be well-disinfected prior to each use. The properties of the polymers used in the lenses allows conventional preservatives and antimicrobials, which might otherwise be used for cleaning and disinfecting, to be absorbed annd concentrated in the lenses and later released when the contact lenses are on the eye. The release of such antimicrobial and preservative materials is generally much slower than the uptake, thereby allowing them to build up in the lenses. This buildup may eventually affect the physical characteristics of the lenses, including their dimension and color. The net result of this process can be the damaging or staining of the contact lens, itself, and/or harming the sensitive conjunctival or corneal tissue in the eye.
Hard contact lenses do not absorb appreciable amounts of water (i.e., only from about 0.1 to about 0.4%) and thus the use of conventional preservatives and antimicrobials generally does not present a problem in the hard contact lens field. Disinfecting of soft contact lenses is frequently carried out by boiling the lenses in normal saline, an inconvenient and cumbersome procedure. Furthermore, wearers of soft contact lenses are often warned that solutions designed for hard contact lenses should not be used with soft lenses, since the preservatives in such solutions will be absorbed and even concentrated by the soft lenses and may seriously damage the contact lens and/or the eye of the user.
Thimerosal (sodium ethylmercurithiosalicylate) and chlorhexidine are well-known preservatives, frequently used in contact lens disinfecting solutions. See, for example, Handbook of Nonprescription Drugs, 5th ed., American Pharmaceutical Association, 1977, pages 236-247, and U.S. Pat. No. Re. 29,693, Phares, reissued July 4, 1978. The use of certain organic acids as components in contact lens cleaning solutions has been disclosed in the art. Japanese Specification No. 78-28,922, Allergan Pharmaceuticals, issued Aug. 17, 1978, describes contact lens cleaning solutions containing polyoxyethylene stearate. French Pat. No. 2,400,906, issued March 23, 1979, describes the use of ascorbic acid and sodium ascorbate in contact lense cleaning solutions.
C.sub.5 -C.sub.12 fatty acids and fatty acid salts are known to be effective antimicrobial and antifungal agents. Keeney, Bull. Johns Hopkins Hosp. 78, 333 (1946), teaches the use of a 20% aqueous solution of sodium caprylate, at pH 7.4, to successfully treat moniliasis. U.S. Pat. No. 2,466,663, Russ, et al., issued Apr. 5, 1949, discloses aqueous solutions, having pH's between 4.5 and 10.5, containing a mixture of caprylic acid and a caprylic acid salt, especially zinc or sodium caprylate. These solutions are taught to be useful in preventing the growth of molds or fungi in foods and other nutrient media. Theodore, JAMA 143, 226(1950), discloses that the lower fatty acids have been shown to be of value in the treatment of external infections of the eyes. Specifically, sodium propionate was found effective against bacteria causing common occular and fungal infections, including staphylococcus and Pseudomonas aeruginosa. Copending U.S. patent application Ser. No. 918,532, Stone, filed June 23, 1978, describes the use of octanoic acid as a broad spectrum antimicrobial agent in intravenous, nutrient and dialysis solutions; these solutions typically contain electrolytes, such as sodium chloride. The antimicrobial benefits of maintaining a solution pH between about 3.5 and 6.0 are taught.
It has now been discovered that when the C.sub.5 -C.sub.12 fatty acids are used in disinfecting solutions (also referred to as sterilization solutions in the art) for soft contact lenses, these solutions provide broad spectrum antimicrobial activity, compatibility with the hydrophilic soft contact lens material, and very rapid and complete desorption of the antimicrobial agent from the contact lens material, thereby minimizing the eye irritation and sensitization problems discussed above.
It is, therefore, an object of the present invention to provide an effective cleaning, disinfecting and storing solution for soft contact lenses characterized by rapid and complete desorption of the antimicrobial material from the lens.
It is a further object of the present invention to formulate aqueous solutions suitable for cleaning, disinfecting and storing hydrophilic soft contact lenses containing C.sub.5 -C.sub.12 fatty acids.
It is a still further object of the present invention to provide a method for cleaning and disinfecting hydrophilic soft contact lenses utilizing C.sub.5 -C.sub.12 fatty acids.